title: Beta-D-xylosidase from Selenomonas ruminantium: thermodynamics of enzyme-catalyzed and noncatalyzed reactions.
abstract: Beta-D-Xylosidase/alpha-L-arabinofuranosidase from Selenomonas ruminantium is the most active enzyme known for catalyzing hydrolysis of 1,4-beta-D: -xylooligosaccharides to D-xylose. Temperature dependence for hydrolysis of 4-nitrophenyl-beta-D-xylopyranoside (4NPX), 4-nitrophenyl-alpha-L-arabinofuranoside (4NPA), and 1,4-beta-D-xylobiose (X2) was determined on and off (k (non)) the enzyme at pH 5.3, which lies in the pH-independent region for k (cat) and k (non). Rate enhancements (k (cat)/k (non)) for 4NPX, 4NPA, and X2 are 4.3 x 10(11), 2.4 x 10(9), and 3.7 x 10(12), respectively, at 25 degrees C and increase with decreasing temperature. Relative parameters k (cat) (4NPX)/k (cat) (4NPA), k (cat) (4NPX)/k (cat) (X2), and (k (cat)/K (m))(4NPX)/(k (cat)/K (m))(X2) increase and (k (cat)/K (m))(4NPX)/(k (cat)/K (m))(4NPA), (1/K (m))(4NPX)/(1/K (m))(4NPA), and (1/K (m))(4NPX)/(1/K (m))(X2) decrease with increasing temperature.
authors.affiliation: US Department of Agriculture, Agricultural Research Service, Fermentation Biotechnology Research Unit, National Center for Agricultural Utilization Research, Peoria, IL 61604, USA. douglas.jordan@ars.usda.gov
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Jordan
authors.forename: Jay D
authors.initials: JD
authors.lastname: Braker
mesh_terms: D006027:Glycosides / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D020357:Selenomonas / Q000201:enzymology*; D013379:Substrate Specificity; D013696:Temperature; D013816:Thermodynamics; D014995:Xylosidases / Q000378:metabolism*
chemical_list: D006027:Glycosides; D014995:Xylosidases; C026579:exo-1,4-beta-D-xylosidase